This invention relates to mobile units employed in a single channel radio communications system. Reference is made to two additional co-pending applications, Ser. Nos. 564,950 and 564,634, filed on the same date as the present application and which contain related subject matter.
Direct mobile-to-mobile radio communication is limited in range by low antenna heights and relatively low power transmitters. In order to overcome these limitations and cover larger geographical areas, the concept of a single channel "community repeater" has developed whereby a receiver is coupled to a higher power transmitter at a location of favorable radio propagation. Signals from a mobile radio transmitter are received by the community repeater receiver and routed to the community repeater transmitter for rebroadcast to receiving mobiles. Many diverse groups of mobile users in the same community can utilize the same "repeater" by transmitting and receiving on the appropriate frequencies. Generally, the type of communication on a community repeater is a "push-to-talk, release-to-listen" message transmission of short duration between one mobile user and a kindred group of at least one other mobile user.
The mobile disclosed herein, in conjunction with the Queued Community Repeater Communications System disclosed in copending application Ser. No. 564,950, resolves the significant user problems encountered when operating on a community repeater system. Crowded conditions can develop on the single communications channel as many different groups consisting of many mobile users attempt to use the channel. Common courtesy is often abandoned as mobile users transmit simultaneously in an effort to capture the channel and communicate their message. Mobile users who listen for a message directed to them or their group are exposed a cacophony of messages which are not of interest and may obscure the desired message.
To improve this situation a number of developments in the mobile equipment, which are now well known, have been made. Mobiles are grouped into formalized "fleets", each with special coding schemes such as continuous subaudible signals or precursor signals which are transmitted by a mobile to activate otherwise muted receivers of other members of its fleet. Directed calls of this sort reduce annoyance to the mobile user, for he no longer has to listen to every message on the channel, but they add to his operating burden as he must monitor the channel before transmitting. Also, even with these developments, access to the channel remains uncontrolled and contentious.
"Trunked" mobile radios used in coordinated multi-channel radio systems have offered better control of communications by being automatically trunked on a plurality of communication channels. Mobile users in these systems must request service from a controller and receive a channel assignment and permission to transmit from the controller before being allowed to transmit on one of the channels. AIthough these systems are effective in reducing contention, the multi-channel. operation protocol used by the mobiles of these systems is simply unusable for a single communication channel.
In addition to mobile radios remote terminals employed in multi-terminal processing have also generated an extensive need for sharing a scarce resource, i.e. a computer processor, among a large number of users. Terminals equipped to operate in time-sharing systems, which have been developed as a result of the need, typically send both a request for service and its message for storage in a queue. The request is subsequently analyzed by an allocation mechanism for eventual assignment of the message to the computer processor. Unlike the present invention, which must coordinate the requesting process with real time message transmission on the single communications channel, the remote terminal transmits its message to the scarce computer processor (which is aloof from the requesting process) for operation in other than real time.
The present invention, for the first time, affords single channel mobile radio users relief from the aggravations of a crowded communications channel. Users' satisfaction improves once contention for this channel is handled automatically and once necessary user manipulations of the mobile to obtain service on the channel are reduced. In addition, channel efficiency is increased as more mobiles can be accomodated on the single communications channel due to the automated control exercised and the reduction of the need to repeat messages due to interference.